What's The Ruling of Applying Substances to Soften the Hair and Dyeing it Black?

As for the substance that makes the hair soft, I do not know of any harm in it, and there is nothing wrong with it.   As for what a woman uses to dye her white hair to become black, this is not permissible, that’s because it is narrated in Sahih Muslim that the Prophet ﷺ said: “Change this gray hair but avoid black.”   The base ruling of commands is [that they are] obligations. And his saying “avoid” is a command. So, the base ruling is that it is obligatory upon us to avoid (dyeing it) black. It’s also because dyeing it black, in reality, opposes the wisdom of Allah The Exalted, for indeed, it is from the wisdom of Allah The Exalted that if a person reaches a certain age, gray hair appears on him.   So, you turning this gray hair black, such that it (i.e. the grayness) is not apparent, means that you have opposed Allah The Exalted in His wisdom regarding this gray hair.   And it is well known that opposing Allah The Exalted in His universal or Islamic command is not permissible for a Muslim.   So, what is obligatory upon the Muslim is that he proceeds in accordance with what Allah The Exalted has decreed, according to what Allah The Exalted has legislated for him.   It is prescribed regarding this matter that a person dyes this grayness with a color other than black. A color, for example, that is between black and yellow, whereby it is brown and not purely black. In this way, the grayness that the person wants to avoid in his hair will be removed and will change to a color that is not forbidden, which is black.